This invention is directed to a molded electrical device comprising an electrically conductive pathway and an insulating material, the device being capable of interconnection with external circuitry, said insulating material comprising a blend of a particular amorphous thermoplastic polymer and a particular crystalline thermoplastic polymer. Also, this invention is directed to a composition suitable for use as an insulating material in an electrical device comprising from about 35 to about 65 weight percent of an amorphous polymer selected from a polyarylethersulfone resin, a polyarylether resin, a polyetherimide, or a polyarylate and from about 65 to about 35 weight percent of a crystalline polymer selected from a poly(arylene sulfide), a polyester, or a polyamide.
It is well known that a wide variety of thermoplastic polymers have been used as substrates for electrical components, such as circuit board substrates. These substrates have been molded from, for example, polyphenyleneoxide, polyphenylenesulfide, polyimide and polyethersulfone. Additionally, the following U.S. Patent Applications disclose substrates made from thermoplastic polymers:
U.S. patent application Ser. No. 516,863, filed in the name of J. E. Harris et al, on July 25, 1983, titled "A Composition Useful For Making Circuit Board Substrates and Electrical Connectors" (commonly assigned) describes a composition useful for making circuit board substrates and electrical connectors comprising a blend of certain proportions of a poly(ether sulfone) and a polysulfone.
U.S. patent application Ser. No. 566,298, filed in the name of H. Chao et al, on Dec. 28, 1983, titled "A Polymer Useful For Molding Into A Circuit Board Substrate" (commonly assigned) describes a select polyarylethersulfone which is useful for molding into circuit board substrates.
U.S. patent application Ser. No. 448,376, filed in the name of J. E. Harris, on Dec. 9, 1982, titled "A Composition Useful For Making Circuit Board Substrates And/or Electrical Connectors" (commonly assigned) describes a composition comprising a blend of a poly(aryl ether), a poly(etherimide) polymer, a fiber and a filler which is useful for making circuit board substrates and/or electrical connectors.
The polymers described above are used as circuit board substrates and in other electrical devices such as chip carriers. These materials are solderable by hand or wave soldering techniques. However, unlike hand and wave soldering, vapor phase soldering (VPS) constitutes a considerably more rigorous form of thermal exposure (as, for example, temperatures of about 420.degree. F., and times of exposure of the substrate of from 30 seconds to in excess of 2 minutes). Unlike wave soldering which involves momentary exposure of the device to temperatures of 500.degree. F., VPS requires that the electrical device be totally immersed in the soldering media. Thus, amorphous resin containing formulations that performed satisfactorily in hand and wave soldering exhibit deficiencies upon VPS exposure, i.e., they exhibit bubbles, blisters, distortion, and foaming. This is attributed to relatively high moisture absorption and low apparent modulus at the VPS processing temperature of the substrate made from amorphous resins.
Crystalline resin systems, on the other hand, have been found to exhibit low moisture absorption and a relatively high modulus at VPS processing temperatures. For example, mineral and/or glass-filled/reinforced poly(ethylene terephthalate) has demonstrated exceptional resistance to bubbling, blistering, and foaming in VPS exposure. However, while possibly suited for making small articles such as chip carriers, filled/reinforced poly(ethylene terephthalate) systems are unacceptable for printed wiring board fabrication due to anisotropic behavior which results in severe bow and warp of the fabricated wiring board. Thus, there is a desire to develop a resin formulation which can be used to fabricate a large variety of molded electrical devices requiring VPS exposure and which maintain their dimensional integrity after VPS exposure.